A period analysis of the optical line variability of Cephei: evidence for multi-mode pulsation and rotational modulation *
J.H. Telting 1, 2,
** 3 and
P. Mathias 4
Received 8 July 1996 / Accepted 31 October 1996
We investigate the optical line-profile variability of the prototype of the Cephei stars. From more than 600 spectra, with a typical signal to noise ratio of over 200 and high spectral resolution, we deduce that the variations show periodicity with at least five different frequencies. We find variability at the previously known frequencies =5.25 cycles/day (radial pulsation) and =5.38 c/d and =4.92 c/d. Additionally, we report two new frequencies =5.08 c/d and =5.42 c/d. These five frequencies are present in periodograms of the velocity moments of all of the absorption lines considered (Si III 4552, 4567, 4574 and O II 4591), and also in periodograms of the intensity variations in these lines.
The variations at frequencies and can be successfully modelled by a radial and a non-radial ( =2 or =1, m =1) pulsation, respectively.
Following results of studies of the UV resonance lines of Cep, we interpret the frequency spacings - 0.33 c/d, - 0.17 c/d, - 0.17 c/d as multiples of the rotation frequency of the star.
We discuss the influence of the presence of a (surface) magnetic field on the apparent modulation of the line-profile variability of the radial pulsation mode.
Key words: line: profiles stars: early-type; oscillations; rotation stars: individual: fi Cep
© European Southern Observatory (ESO) 1997
Online publication: June 5, 1998